The ASE T2 Diesel Engines test has 55 scored questions in eight content areas, plus 10 unscored questions, and you get 90 minutes for all 65. It belongs to ASE's Medium/Heavy Truck series, for technicians who work on Class 4 through Class 8 trucks and tractors. Fuel system diagnosis and repair is the biggest area at 16 questions (29.1%), then general engine diagnosis at 11 (20.0%), so those two make up 27 of the 55. Lubrication and cooling and air induction and exhaust have 6 each (10.9%), the engine block has 5 (9.1%), the cylinder head and valve train and starting and charging have 4 each (7.3%), and engine brakes have 3 (5.5%). Every question ties to one or more tasks in ASE's task list. Questions are four-option multiple choice, including symptom-to-cause, EXCEPT and Technician A / Technician B items. T2 is one of the seven tests, T2 to T8, for Master Medium/Heavy Truck Technician.
01The test specification
The ASE test specification for ASE T2 Diesel Engines splits the 55 scored questions across eight content areas. ASE adds 10 unscored questions for research, and you have 90 minutes for all of them. Each area links to five free questions.
| Area | Content area | Scored questions |
|---|---|---|
| A | General Engine Diagnosis | 11 (20%) |
| B | Cylinder Head and Valve Train Diagnosis and Repair | 4 (7.3%) |
| C | Engine Block Diagnosis and Repair | 5 (9.1%) |
| D | Lubrication and Cooling Systems Diagnosis and Repair | 6 (10.9%) |
| E | Air Induction and Exhaust Systems Diagnosis and Repair | 6 (10.9%) |
| F | Fuel System Diagnosis and Repair | 16 (29.1%) |
| G | Starting and Charging System Diagnosis and Repair | 4 (7.3%) |
| H | Engine Brakes | 3 (5.5%) |
| Total | 55 |
02What is the ASE T2 Diesel Engines test?
T2 is ASE's Diesel Engines test in the Medium/Heavy Truck series, the tests for technicians on Class 4 through Class 8 trucks and tractors. Its task list covers the whole diesel engine: diagnosis on and off the road, the cylinder head and valve train, the block and rotating parts, lubrication and cooling, air induction and exhaust (aftertreatment and EGR included), the fuel system and its electronic controls, starting and charging, and engine brakes.
It has 55 scored questions and 10 unscored ones, 65 in all, and you get 90 minutes. Every question is multiple choice with four options, (A) to (D). ASE puts the 10 unscored questions on every certification test to gather statistics for future tests, and you cannot tell which ones they are, so answer every question.
Passing is one half of certification. ASE also asks you to document relevant work experience, which for tests in this series is 2 years, and its study guide says suitable vocational training may count toward it; the details are at workexp.ase.com. The study guide does not publish a passing score.
T2 is one of the seven tests, T2 to T8, that you need to pass for ASE to recognize you as a Master Medium/Heavy Truck Technician, according to its truck study guide. T1 Gasoline Engines is in the same series but is not on that list. T2 does not count toward Master Automobile Technician.
03What does each content area cover?
Area A: General Engine Diagnosis (11 questions)
Eighteen tasks. The list starts where any diagnosis starts: confirm the complaint on a road test or a dyno, talk to the driver, read the maintenance records, and use the engine model, serial number or EPA certification level to find the right service information and bulletins. Then come the inspections: leaks of fuel, oil, coolant, exhaust and DEF, harness routing and condition, noise and vibration, and the exhaust itself, judged by smoke color, odor, volume and opacity. A run of tests follows: fuel supply and return, intake restriction and leaks, intake manifold pressure, exhaust back pressure and temperature along with soot and ash load, and crankcase pressure on open and closed systems.
The symptom tasks cover an engine that will not crank, cranks and will not start, starts hard hot or cold, or starts and then dies, plus surging, rough running, misfire, low power, slow response and shutdowns. You also check the coolant, the oil (including reading an oil analysis report) and the DEF for condition, level, temperature and pressure, connect a diagnostic tool to check the calibration, codes and trip data, confirm the repair and the programmable parameters, and look for damaged, missing, modified or tampered parts.
Area B: Cylinder Head and Valve Train Diagnosis and Repair (4 questions)
Eleven tasks. You remove, strip and clean the head, check its threads, studs and bolts, measure its thickness, check mating surfaces for warpage and finish, and look for cracks and the state of the passages and plugs. The valve parts include rotators as well as guides, seats, springs, retainers, locks and seals. Two diesel jobs stand out: injector sleeves and seals, with a pressure test where it applies and a check of injector tip or nozzle protrusion when the maker specifies one, and valve bridges, also called crossheads. The list ends with pushrods or push tubes, rocker arms and shafts, cam followers, valve lash and injector settings, and the overhead camshaft with its bearings, endplay and backlash.
Area C: Engine Block Diagnosis and Repair (5 questions)
Nineteen tasks, the longest list on the test, for 5 questions. It covers the block itself (cracks, warpage, deck height, passages and plugs, threaded holes and dowels), the counterbore and lower bore, and liners: measuring them for wear and cavitation, replacing liners and seals, and setting liner height or protrusion. Then the in-block camshaft, its bearings and followers; the crankshaft, its journals, the main bearings, clearances and endplay; and timing the gear train, with gear backlash and the engine position and speed sensing parts.
Pistons, pins, rings and rods follow: piston-to-wall clearance, ring end gap and groove fit, piston height, rod bearing clearance, bearing wear patterns that point to rod, crankshaft or bore problems, and the piston cooling nozzles. The list closes with the vibration damper, aligning the flywheel housing, flywheel or flexplate runout and ring gear, and block heaters and auxiliary coolant heaters.
Area D: Lubrication and Cooling Systems Diagnosis and Repair (6 questions)
Fourteen tasks split between oil and coolant. On the oil side: checking pressure and temperature along with their sensors and gauge, the oil pump and its drive, regulator and bypass valves, the oil cooler and oil thermostat, oil supply and cooling for the turbocharger, and an oil and filter change with the right oil in the right amount. On the cooling side: belts, pulleys and tensioners; coolant temperature and level sensors; thermostats and restrictors; flushing, refilling and bleeding with the right coolant and recovering the old; the coolant filter or conditioner; the water pump; pressure testing the system, caps and tanks; and the fan, fan clutch, fan controls and shroud, along with airflow through the cooling package.
Area E: Air Induction and Exhaust Systems Diagnosis and Repair (6 questions)
Eight tasks, several of them broad. On the intake side: the air cleaner, piping, restriction indicator and housing drain valve, the intake manifold and its sensors, and the charge air cooler. Turbochargers, fixed and variable, with their pneumatic, hydraulic or electronic actuators and wastegates, calibrated where required. On the exhaust side: manifolds, piping and mufflers. Cold-start aids: grid or inlet air heaters and glow plugs. Two tasks carry most of the emissions content: the aftertreatment system (hydrocarbon doser, DOC, DPF, DEF and SCR, and checking that regeneration works) and the EGR system, from the valve and cooler to its differential pressure sensors and wiring.
Area F: Fuel System Diagnosis and Repair (16 questions)
Fourteen tasks for 16 questions, the only area with more questions than tasks. The low-pressure side comes first: tanks, vents and lines, the transfer pump and its drive, fuel/water separators, filters, heaters and coolers (ECM cooling plates included), checking for leaks, air and contamination, priming and bleeding, and the check valves and regulators that control low-side pressure. The high-pressure side covers injection lines and transfer tubes, then on-engine tests of the three injection systems the task list names: high-pressure common rail, hydraulic electronic unit injectors (HEUI) with their rail pressure control, and electronic unit injectors (EUI).
The rest is electronic: throttle and engine speed controls; engine protection, derate and shutdown; connectors and harnesses; using a scan tool to check and update calibrations, injector calibration codes and programmable parameters and to run relearns; testing sensors, actuators, control modules and circuits; and reading voltage, voltage drop, current and resistance with a multimeter or oscilloscope.
Area G: Starting and Charging System Diagnosis and Repair (4 questions)
Seven tasks: identify the battery type and test its state of charge, load and capacity; charge it the right way; jump start with cables, a booster battery or an auxiliary supply; clean and replace batteries, cables, extra ground cables and terminals; test the starter, relays, safety switch and solenoids; test alternator voltage and current output and its remote sense circuit; and run voltage drop tests on the starting and charging circuits.
Area H: Engine Brakes (3 questions)
Three tasks, one per question, all on compression and exhaust brakes: test and adjust the brake itself; work on its control circuits, switches, actuators and solenoids and set its control parameters; and repair the housing, valves, seals, springs and lines and adjust them to spec.
04What kind of questions are on it?
ASE's truck study guide has nine T2 sample questions. Most start from a symptom and ask what could cause it: coolant pushed out of the overflow with bubbles in the radiator under load, heavy black smoke on a morning start, a no-start on a HEUI engine, an engine that is hard to start until it has been primed and run, and a wet-liner engine that runs hot with coolant in the crankcase. For these, work out which system the symptom points to before you weigh the options. In the samples, the wrong options are plausible faults too, often from the same system, so pick the one that explains every part of the symptom.
One sample is a straight knowledge item: what you change to set cylinder liner protrusion. That ties to the liner tasks in area C, so know the measurements and how each is corrected, not only what they are called.
One sample is an EXCEPT question about an electronically controlled engine that will not start. ASE flags these with a line telling you the question contains the word EXCEPT, and you are looking for the one option that could not cause the problem. Read every option against the symptom, since three of them are true.
Two samples are Technician A / Technician B items: one on what to do after repairing the cause of a logged fault code, and one on low boost with low power. In both, only Technician A was right, a reminder that each statement must be judged on its own. See how to answer Technician A / B questions.
05Where should your study time go?
Area F, the fuel system, is 16 of the 55 scored questions (29.1%), the largest single area. With general engine diagnosis in area A, areas F and A are 27 of 55 (49.1%). Adding lubrication and cooling (area D) and air induction and exhaust (area E), 6 questions each, brings it to 39 of 55 (70.9%). The other four areas, B, C, G and H, share the last 16 questions (29.1%).
Start with area F and give each injection system its own session: common rail, HEUI and EUI, then the electronic tasks (scan tool, calibrations, sensors and meter readings). Area A comes next. Its checks of fuel, intake, exhaust, crankcase pressure, coolant and oil are diagnostic tests on the same systems areas D, E and F cover, so study them alongside those areas. Area C has 19 tasks for 5 questions, so cover its liner, crankshaft and piston measurements without trying to memorize every detail. Area H has 3 tasks for 3 questions, a short list worth knowing completely.
Use the task list as a checklist and mark each task you could explain. ASE says every question represents one or more tasks, though any one version of the test may leave some of them out. Pace: 65 questions in 90 minutes is about 1 minute 23 seconds each.
06Registering, retesting and recertifying
You register and pay through ase.com. ASE charges a $34 registration fee per order plus $62 for each test, so T2 on its own comes to $96, and each extra test in the same order adds $62. Fees and dates can change, so check ase.com before you book. The full breakdown is in ASE test fees and registration.
The test is delivered on screen. ASE offers a free demo of its testing platform at ase.com/free-test-drive, and the truck study guide notes that every ASE test has a pop-up English to Spanish glossary. More on the format: how ASE tests work.
ASE's general rules, which the truck study guide does not repeat, are a 30-day wait before you can retake a test you did not pass and a certification period of 5 years; confirm both for T2 on ase.com. If you need the retest, put the month into area F first, then area A.
To renew the certification you take the T2 recertification test, 28 questions in 45 minutes. You are eligible for it only after passing the full T2 certification test once.
07Questions people ask
- How many questions are on the ASE T2 Diesel Engines test?
- 65 questions in 90 minutes: 55 scored and 10 unscored. ASE uses the 10 unscored questions to gather statistics for future tests, and you cannot tell which ones they are, so answer all 65. That is about 1 minute 23 seconds per question.
- What is the biggest content area on ASE T2?
- Fuel System Diagnosis and Repair, with 16 of the 55 scored questions (29.1%). General Engine Diagnosis is next with 11 (20.0%). Together they are 27 of the 55 scored questions.
- Does ASE T2 count toward Master Technician?
- Yes, for the truck series. ASE lists T2 to T8, seven tests, as required for recognition as a Master Medium/Heavy Truck Technician; T1 is not on that list. T2 does not count toward Master Automobile Technician.
- What score do you need to pass ASE T2?
- ASE's study guide does not publish a passing score for T2. It publishes the content areas, the question counts and the task list. Check ase.com for how results are reported.
- How long is the ASE T2 recertification test?
- The T2 recertification test has 28 questions in 45 minutes, against 65 questions in 90 minutes for the T2 certification test. You can take it only after passing the full T2 certification test once.
- Is ToolboxPrep affiliated with ASE?
- ToolboxPrep is an independent study site, not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original, written from ASE’s published test specifications and task lists and other public sources. They are not actual ASE test questions and not recalled or “brain dump” questions. ASE is a trademark of its owner, and we never use the ASE logo. Standards and service information are cited, not reproduced.
08Sources
- ASE Medium/Heavy Truck Study Guide (Tests T1 to T8), 2026: the T2 test specification, question counts, testing time, the 10 unscored questions, the task list this page paraphrases, the sample-question formats, the 2-year work experience requirement, the Master Medium/Heavy Truck Technician test list and the glossary
- ASE (ase.com): the $34 registration fee per order, the $62 fee per test, the 5-year certification period, the 30-day retest wait and the T2 recertification test length
The content areas and question counts were checked against ASE's published study guide on October 17, 2026, and the task descriptions paraphrase its task list. ASE's study guide is the final word. If you find one of ours out of date, tell us.
Related: free practice questions · ten free T2 questions · How ASE tests work · ASE test fees and registration
09Practice for this test
ToolboxPrep T2 practice tests are weighted to the specification above, area by area, and every answer is explained, all four options. You can try five sample questions with no account.
Ten free questions per test, no account: free practice questions. How our questions are written and checked: how our questions are made.
ToolboxPrep is an independent study site, not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original, written from ASE’s published test specifications and task lists and other public sources. They are not actual ASE test questions and not recalled or “brain dump” questions. ASE is a trademark of its owner, and we never use the ASE logo. Standards and service information are cited, not reproduced.